The use of whitening agents to impart a higher degree of whiteness to goods such as paper, paperboard, textiles and nonwoven fabrics is well known. The most widely used whitening agents in the field of paper and cardboard are the derivatives of 4,4′-bis-[1,3,5-triazinyl]-diaminostilbene-2,2′-disulfonic acid substituted at the triazine ring with anilino and alkanolamino groups. The anilino groups may contain other sulfonic groups, but since these groups increase the solubility in water of the related molecules, they also reduce the affinity of the molecules towards the cellulose fibres that make up the paper so that they lead to inferior performance in terms of the degree of whiteness.
For reasons of ease of processing, the paper industry requires that these whitening agents are provided in the form of liquid fluid aqueous dispersions or, most preferably, of an aqueous solution stable for at least several months at temperatures from 5 to 40° C.
The stilbene whitening agents that are derivatives of 4,4′-bis-[1,3,5-triazinyl]-diaminostilbene-2,2′-disulfonic acid substituted at the triazine ring with anilino groups and alkanolamino groups, preferred in this field, are not readily soluble in water, hence the production of the relevant concentrated and stable aqueous solutions has required in the past the addition of significant amounts, even up to 30%, of solubilizing agents such as urea, caprolactame, ethylene glycol and polyglycols.
However, the added solubilizing agents does not have a great affinity for cellulose and do not contribute significantly to the performance of the product resulting in undesirable pollutants, at the end of the process of paper production. For example, in the case of use of whitening agents solutions formulated with urea, a strong additional polluting load consisting of nitrogen-based by-products and ammonia is introduced in the liquid effluents of the process.
A further problem derives from the inevitable presence in the whitening agents solutions of inorganic chlorides, for example sodium chloride, which is derived from the synthesis processes of the whitening agents. In fact, all the industrial processes of production of stilbene whitening agents substituted with triazine involve the use of cyanuric chloride as a reagent, which reacts in successive stages with different required amino products inevitably leads to generation of large quantities of inorganic chlorides that are difficult to eliminate.
The remaining inorganic chlorides generate instability in aqueous whitening agents concentrated solutions so that it is essential to significantly reduce the content thereof, inevitably using costly osmotic separation techniques, to obtain compositions that remain stable for a long time.
U.S. Pat. No. 3,012,971 discloses compositions for the bleaching of paper formed of concentrated aqueous solutions of 4,4′-bis-[2-phenylamino-4-diethanolamino-1,3,5-triazinyl]-diaminostilbene-2,2′-disulfonic acid or a salt thereof in admixture with alkanolamines, wherein the proportion by weight of alkanolamines with respect to the whitening agents varies from 0.5:1 to 3.0:1. Since the molecular weight of alkanolamines is much lower than that of the whitening agents, said range defines a large excess of alkanolamine compared to the whitening agent. However, such high amounts of alkanolamines, compared to the whitening power of the composition, are not acceptable from the ecological point of view.
WO 2005/028749 discloses aqueous compositions comprising stilbene whitening agents and alkanolamines. This document does not describe any example of a composition comprising a tertiary alkanolamine. In addition, there is no mention of the problem of the effect of inorganic chlorides on the stability of the solution.
U.S. 2010/0159763 describes aqueous compositions of fluorescent whitening agents, substituted to the triazine rings with propionamide amino groups, having the following formula:

wherein at least 25% of the [M+] ions associated with the sulfonic group have been replaced by (CH3)2NH+CH2CH2OH ions. However, in order to guaranteeing the stability of the formulation, it is necessary in such compositions to reduce the content of inorganic salts by suitable osmosis processes.
IT 1356016 discloses a method for the optical whitening of the paper through the use of substantially aqueous suspension of the compound having the following formula:

wherein M and M1 represent hydrogen, an alkali metal, an alkaline earth metal or ammonium.